Filter device, in particular for high-pressure applications in a molten polymer filtration

ABSTRACT

A filter device, in particular, for high-pressure applications in a molten polymer filtration, has a screw-in piece ( 10 ), provided with a first threaded section ( 12 ) for fixing the filter device, and a second threaded section ( 14 ) for fixing a filter medium ( 16 ), in particular, in the form of a metal wool and with a perforated support tube ( 18 ) for the metal wool. The other free end of the filter device is provided with a volume displacer ( 24 ). The metal wool is surrounded by a support grid ( 20 ) and fixed by two fixing pieces ( 28, 30 ), held at a separation from each other by the support grid ( 20 ). One fixing piece ( 28 ) is fixed to the second threaded section ( 14 ) of the screw-in piece ( 10 ). The other fixing piece forms a handle ( 30 ) for the fixing formed. As a result of the volume displacer ( 24 ) being a one-piece component of the support tube ( 18 ) and the fixing piece ( 30 ) forming the handle covering the volume displacer ( 24 ), the filter device is significantly improved in that a simple and rapid assembly procedure for the exchangeable filter medium is provided. Also, the filter element construction is held formed to be free of damaging torsional loads.

FIELD OF THE INVENTION

The present invention relates to a filter device, in particular, forhigh-pressure applications in a molten polymer filtration, having ascrew-in component provided with a first threaded section for fixing thefilter device and a second threaded section for fixing a filter medium,in particular, in the form of metal wool. The metal wool has aperforated supporting tube. The other free end of the filter device isprovided with a volume displacement component. The metal wool isenclosed in a support grid and retained by two fixing components spaceda certain distance from each other by the support grid and fixed on thesecond threaded section of the screw-in component. One fixing componentforms a handle.

BACKGROUND OF THE INVENTION

WO 90/00434 discloses an annular flange between the first and secondthreaded section of the screw-in component. An annular seal may besupported on the annular flange and brought into contact by its otherannular surface with the screw-on fixing component of the filter medium.The fixing component is provided on its outer circumference withsetscrews positioned diametrically opposite each other to facilitate thescrew-on process. The opposite side of the filter medium is fixed to asecond fixing component. The second fixing component also has on itsouter circumference screw-in openings positioned diametrically oppositeeach other for applying a fixing tool, so that it is possible to use thefixing tool and the auxiliary fixing means in the form of the setscrewsto carry out a screw-on application process potentially free of torsion.In this way, the filter medium, in particular, one in the form of metalwool, is kept free of torsional stresses for later polymer meltfiltration, and avoids damaging the support grid enclosing the metalwool filter medium to shield it from the exterior. The volumedisplacement component is then screwed onto this fixing component in thedirection of the supporting tube. While this disclosed solution doesmake it possible to replace a fouled filter medium with a new filterelement having fixing components and to leave the valuable stainlesssteel components in the form of the screw-in component and thesupporting tube at the place of assembly, the assembly process itself isdifficult to carry out because of insufficient rigidity of the filterelement structure which complicates the replacement process. Thepossibility of buildup of torsional stresses in the support grid and inthe filter medium in the fixing processes, make failure possible,especially in a high-pressure application.

DE 43 43 270 A1 discloses a spinning head for spinning polymer melts,having an upper element and a nozzle block housing with a nozzle platehaving a maximum area of 90 cm² and a melt channel with filtercartridge. As disclosed, a single filter cartridge is mounted upstreamin the direction of flow from each nozzle plate. The filter cartridgehas a seamless wire cloth cylinder through which flow proceeds radiallyfrom the exterior toward the interior. The cylinder has a cap at theupper end and a connecting piece tapering downward through which melt isconducted at the lower end. The zone of the melt channel receiving thefilter cartridge is configured as a cone, at least in the lower third.The tapering connecting piece of the filter cartridge is pressed intothe cone by the polymer melt so as to be self-sealing. Uniform flow ofthe polymer melt with dead spaces eliminated is achieved to the greatestextent possible. A volume displacement component, which is a one-piececomponent of a supporting tube for the filter medium, is provided at theupper end of the filter cartridge, opposite the lower end of the conereferred to. Despite the resulting reinforcement of the system as awhole, susceptibility to torsional stresses is still present. On thewhole, the process of filter element replacement is accomplished onlywith difficulty. Virtually complete disassembly of the disclosedspinning head is required for the purpose.

WO 01/52966 A1 discloses a filter device with a filter housing having afilter admission and filter discharge, as well as a filter elementdividing a filter chamber into two component chambers. Since onecomponent chamber narrows in cross-section from the filter admissiontoward the filter discharge, a conical configuration of at least one ofthe two component chambers separated by the filter element is provided.This configuration permits achievement of optimal dwell timedistribution inside the filter device, along with a uniform rate offlow, a characteristic which performs an essential function, especiallyin the case of high-viscosity fluids such as polymer melts. A fixingcomponent configured as a handle encircles the volume displacementcomponent in the interior. Since the filter medium surrounding thesupporting tube rests on the fixing component and at the opposite end inreceptacle components is rigidly connected to the housing, the harmfultorsional stresses described also arise in a process of disassembly andreplacement of the filter element. Replacement of the filter elementsalso entails high cost.

SUMMARY OF THE INVENTION

Objects of the present invention are to provide an improved filterdevice permitting simple and rapid assembly of the filter medium to bereplaced, as well as keeping the filter element design free of harmfulstresses, especially ones in the form of torsional stresses.

These objects are basically attained with a filter device where thevolume displacement component is an integral component of the supportingtube and the fixing component configured as a handle encircles thevolume displacement component. Consequently, the volume displacementcomponent as a component of the supporting tube no longer diminishes theoperating cross-section for the fixing component configured as handle.This fixing component is then reinforced as a sealing or cover componentto the extent that a rigid structure is achieved for the filter elementas a whole as replacement modular unit. Thus, torsional forces harmfulto the filter medium in the fixing or screw-on process may be largelyprevented. A screw-in cartridge of stable configuration is obtained. Thecostly volume displacement component may remain in the supporting tubein a replacement process and need not be removed in a detailed process.The solution of the present invention also makes it possible to carryout the fixing and exchange process exclusively by the handle, so thatadditional auxiliary assembly components such as setscrews or the likemay be entirely omitted on the other fixing component with the threadedsection.

In one preferred embodiment of the filter device of the presentinvention provision is also made such that, when the screw-in componenthas been introduced, an annular seal, in particular, one in the form ofa metal wool seal, is mounted between the first and the second threadedsection of the fixing component. A separate annular seal on an annularflange of the screw-in component, provided in conventional designs, maybe completely omitted. Yet, reliable sealing is thereby achieved.

In another, especially preferred, embodiment of the filter device of thepresent invention, the filter medium is retained by projections ofmaterial, especially also by indentations of the fixing components, atspecified fixing points. The fixing points preferably represent anintegral component of the fixing components. The respectiveconfiguration provides for a torsion-free fixing and replacement processfor the filter medium, so that this medium is kept largely free ofharmful material stresses.

In another preferred embodiment of the filter device of the presentinvention, the fixing component serving as handle has the filter devicespaced a certain distance axially from the volume displacementcomponent. This volume displacement component is provided with slopingsupport surfaces which are at least to some extent in contact withsupporting surfaces of the handle when a fixing component has beenscrewed in. The respective configuration, with the volume displacementcomponent resting on the handle, provides security of contact makingcertain that the threading of the fixing component to be screwed on willnot be screwed on too tightly, a condition which could damage thethreading. Contact is also established such that the metal wool asfilter medium, together with its support grid, is not subjected toharmful torsional forces.

Other objects, advantages and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, discloses preferredembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a diagrammatic (not to scale) side elevational view of afilter device, partly in section, according to a first embodiment of thepresent invention;

FIG. 2 is an end elevational view in section taken along line I–I inFIG. 1; and

FIG. 3 is a diagrammatic (not to scale) side elevational view, partiallyin section, of a filter device according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The filter device according to the present invention in the firstembodiment shown in FIGS. 1 and 2 is explained first. The secondembodiment will then be presented, but only to the extent that itdiffers essentially from the first embodiment.

The filter device is provided, in particular, for high-pressure use inpolymer melt filtration. The filter device has a screw-in component 10for fixing the filter device in an overall filter module (not shown) andhaving a first threaded section 12. The screw-in component 10 also has asecond, downstream, threaded section 14 for fixing a filter medium 16,in this instance a metal wool suitable for polymer melt filtration. Inthe interior, the filter medium 16 rests on a perforated supporting tube18. On the outside, the metal wool or filter medium 16 is enclosed in asupport grid 20 with rectangular passage areas 22. The supporting tube18 is rigidly connected on one of its ends to screw-in component 10,especially by a welded connection. On its other free end, the supportingtube is connected to a volume displacement component 24, particularly bya welded seam. The volume displacement component 24 is engaged by itstapering fluid conducting component in the supporting tube 18, and thus,serves to even out the polymer melt flow inside the supporting tube inthe direction of the discharge opening 26 inside the screw-in component10.

Both the support grid 20 and the filter medium 16 are retained on twofixing components 28, 30 kept at the specified distance between them, inparticular, by the filter medium 16. The first fixing component 28secures the filter medium 16 on the second threaded section 14 of thescrew-in component 10. The second fixing component 30 is provided as ahandle for the fixing process involved. The overall structure of fixingcomponents 28, 30, with support grid 20 and filter medium 16, isaccordingly configured so that a process of screwing in and unscrewingof the respective filter unit is made possible essentially by engagementof the handle in the form of the second fixing component 30. Thedirection provided for passage of the polymer melt, especially at highpressure values, extends from the exterior toward the interior,initially by the support grid 20, then by the filter medium 16 andperforations in the supporting tube 18 to the interior of the filterdevice. The polymer melt then leaves the filter device by the dischargeopening 26 for subsequent use after impurities have been removed from itin this manner. If the metal wool is added as filter medium 16 removingimpurities, the possibility accordingly exists of making a new filtermedium available for repeated use by the handle 30, by detaching thescrew-in component 10 by the first fixing component 28. Since the secondfixing component 30 more or less encloses the volume displacementcomponent 24, the handle may be designed to be highly rigid, a conditionfavoring the overall rigidity for the replacement components. Harmfultorsional stresses, especially those arising in the fixing process, maybe kept away from the filter medium with its support grid 20.

An annular seal 32 is mounted between the first threaded section 12 andthe second threaded section 14 of the screw-in component 10. Annularseal 32 is on the free frontal surface of the first fixing component 28after this component has been introduced, in particular, a seal in theform of a metal wool seal. This arrangement presents the advantage thatthe filter element, which has only one seal, is kept replaceable and yetreliable sealing of the interior of the filter device from thesurroundings is provided in this way during later use. Unintended escapeof the polymer melt is accordingly reliably prevented, even in decidedlyhigh-pressure applications.

The filter medium 16 is retained in specific fixing positions inrecesses in the fixing components 28, 30 by projections of material, inparticular, in the embodiment shown in FIG. 1. The inherently flexiblemetal wool as filter medium 16 may thus be fixed to the projections ofmaterial 34 by pressing processes. This fixing technique may be costeffectively applied, and yet permits reliable fixing. The fixingpositions referred to are themselves integral components of the fixingcomponents 28, 30. The respective fixing position continues as anextension in the fixing component 28, 30. The latter also promotes theoverall reinforcement of the system. As shown in FIG. 2, in particular,the filter medium 16 extends in pleated form around the supporting tube18, and is enclosed toward the exterior by the support grid 20.

The second fixing component 30 serving as handle is spaced a certaindistance 36 in the axial direction of the filter device from the volumedisplacement component 24. The volume displacement component 24 isprovided with tapering support areas 38 which are at least to someextent in contact with support surfaces 40 of the second fixingcomponent after the first fixing component has been introduced. Asupporting force may thus be exerted on the volume displacementcomponent 24 during the screw-in process. The volume displacementcomponent 24 may then also serve as a backing to prevent excessivetightening on the threaded sections in the area of the first fixingcomponent 28. In addition, forces arising during filtration may then bereliably diverted by the support areas 38, 40 into the base structure ofthe supporting tube 18 with screw-in component 10. The latter alsocontributes to reinforcement of the system as a whole, so as to providethe possibility of shielding the filter medium 16 itself from theeffects of harmful forces.

The second embodiment is described in detail with reference to FIG. 3.The same reference numbers are employed as those used for the firstembodiment. The second embodiment will accordingly be explained only tothe extent that it differs from the first embodiment illustrated inFIGS. 1 and 2.

First of all, in the second embodiment shown in FIG. 3, the fixingcomponent 30 serving as handle is provided with a tapered element 42extending outward toward the exterior. In addition to fixing of thefilter device by the screw-in component 10, the tapered element 42 alsoprovides the option of fixing inside an overall filter device (notshown), in addition to that of fixing the filter device by the screw-incomponent 10. In addition, each of the first and second fixing component28, 30 has two sections 28 a,b, 30 a,b, each of the respective sectionsbeing rigidly connected to each other by a weld seam. The respectivesection 28 b, 30 b has a corbel projecting inward. The filter medium 16is thickened by a built-up weld seam so that the weld seam overlaps thesection so that the filter medium 16 may be fixed on the sections 28 b,30 b. This arrangement provides a very slim overall filter device inwhich the support grid 20 more or less determines the outer diameter ofthe overall filter device.

Both embodiments have in common the feature that the screw-in component10 forms with the supporting tube 18 and the volume displacementcomponent 24 a module present on an overall filter unit and that thefilter medium 16 with its two fixing components 28, 30, which is subjectto wear, is separable as replacement module from the fixed module. Ifthe filter device is used for filtration of polymer melts, all essentialstructural components are made of stainless steel materials.

While various embodiments have been chosen to illustrate the invention,it will be understood by those skilled in the art that various changesand modifications can be made therein without departing from the scopeof the invention as defined in the appended claims.

1. A filter device, comprising: a first module including a screw-incomponent with a first threaded section for mounting the filter deviceand with a second threaded section, including a perforated supportingtube fixedly attached to and extending from said screw-in component at afirst axial end of said supporting tube, and including volumedisplacement component fixedly attached to said supporting tube at to asecond axial thereof to form an integral component end of saidsupporting tube; and a second module including a metal wool filtermedium, including a support grid enclosing said filter medium andincluding first and second fixing components retaining and fixed to saidsupport grid and said filter medium and spaced from one another by saidsupport grid and said filter medium, said first fixing component beingthreadedly coupled to said second threaded section of said screw-incomponent, said second fixing component forming a handle formanipulating the filter device and encircling said volume displacementcomponent, said filter medium encompassing and being supported on aninterior thereof by said support tube.
 2. A filter device according toclaim 1 wherein the filter device is for high pressure applications inmolten polymer filtration.
 3. A filter device according to claim 1wherein an annular seal is mounted between said first and secondthreaded sections of said screw-in component and on a free frontalsurface of said first fixing component.
 4. A filter device according toclaim 3 wherein said annular seal is a metal wool seal.
 5. A filterdevice according to claim 1 wherein said fixing components haveprojections retaining said filter medium thereto.
 6. A filter deviceaccording to claim 5 wherein said fixing components comprise recessesreceiving said filter medium to retain said filter medium with saidprojections.
 7. A filter device according to claim 5 wherein each saidprojection is an integral extension of the respective fixing component.8. A filter device according to claim 1 wherein said second fixingcomponent is spaced a certain distance in an axial direction of thefilter device from said volume displacement component; and said volumedisplacement component comprises tapering support areas at leastpartially in contact with said second fixing component.
 9. A filterdevice according to claim 8 wherein said second fixing componentcomprises a tapered element engaging said tapering support areas.
 10. Afilter device according to claim 5 wherein said first fixing componentcomprises first and second interconnected sections, said firstinterconnected section having a thread engaging said second threadedsection, said second interconnected section having said projectionthereof.
 11. A filter device according to claim 10 wherein said firstand second interconnection sections are fixed to one another by a weldseam.
 12. A filter device according to claim 1 wherein said first moduleis a lasting structural unit; and said second module is a replacementunit subject to wear.
 13. A filter device according to claim 1 whereinsaid first and second modules are formed of stainless steel materials.14. A filter device according to claim 1 wherein said second fixingcomponent laterally surrounds and directly engages said volumedisplacement component.
 15. A filter device according to claim 14wherein said second fixing component and said volume displacementcomponent have mating tapering support areas that engage one another.